Telecommunication services of the wire-free interactive type are developing rapidly. These services relate to telephony, facsimile transmission, television, in particular digital television, the so-called "multimedia" sector and the internet network. The equipment for these mass-market services has to be made available at a reasonable cost. This is so, in particular, as regards the user's receiver/transmitter which has to communicate with a server, most often via a telecommunication satellite, or in the scope of an MMDS (multi-point multi-channel distribution system), LMDS (local multi-point distribution system) or MVDS (multi-point video distribution system). These communication methods generally use the microwave range. For example, in the scope of the MMDS, frequency bands of the order of 40 GHz are used.
For these frequency ranges, a waveguide receiver and a wavelength transmitter can be used, the two waveguides being separate.
FIG. 1 represents a diagram of a device 1 for the transmission/reception of signals, in general located outside a dwelling (not shown). This device 1 comprises, on the one hand, a reception antenna 2, connected by a reception path 3 to a unit 4 for conversion to intermediate frequency and, on the other hand, a transmission antenna 5, connected by a transmission path 6 to a unit 7 for frequency conversion to a higher frequency. The two units 4, 7 are connected by a coaxial cable 80 to a set inside the dwelling. Each unit 4, 7 respectively comprises a mixer 4.sub.1, 7.sub.1 connected to a local oscillator 4.sub.2, 7.sub.2. The transmission antenna makes it possible to employ a return path to the transmitter.
The device which has just been described has the disadvantage of requiring, in particular, two local oscillators in the conversion units 4, 7 of the outside set, one for reception and the other for transmission.